Bang Bang! is an action romantic thriller and the remake of the 2010 Hollywood film Knight And Day. The movie follows the story of a mysterious man named Rajveer Nanda (Hrithik Roshan) who steals the Koh-i-Noor diamond, one of the most expensive diamonds in the world. Rajveer is continuously chased by underworld gangster Omar Zafar (Denny Denzongpa) who is after the diamond. Rajveer accidentally meets an ambitious bank receptionist, Harleen Sahni (Katrina Kaif) who leads a boring life that suddenly takes a turn and unknowingly becomes part of this adventurous yet dangerous theft.